His comments came as Deputy Chief Constable Judith Gillespie ruled herself out of the race to succeed Matt Baggott as Chief Constable in a staff email.

The controversy over the job erupted after Justice Minister David Ford said he would remove the mandatory requirement for applicants to have served two years at senior rank outside Northern Ireland.

The DUP and Sinn Fein told Mr Ford he was not entitled to take such a decision alone, and referred it to the full Executive.

Now documents seen by this paper have cast doubt on claims by Sinn Fein and the DUP that Mr Ford unilaterally changed the criteria for appointing a new Chief Constable after the process began.

In his letter to Policing Board members, Mr Pollock wrote: "I am disappointed in the fact that board members, in my view, have been commenting inappropriately and in a way that damages their independence and objectivity should such members be engaged in a few weeks' time in appointment processes based on absolute fairness and impartiality."

He added: "Following the decision of the Chief Constable to announce his departure, media commentary and speculation is potentially damaging, and is impacting on the confidence and integrity of the board as a public body in fulfilling its statutory duties."

He made clear that, contrary to suggestions, the process of replacing Mr Baggott was not yet under way and the criteria for his replacement had not been settled.

He wrote: "The appointments processes for Chief Constable and the Deputy Chief Constable will be initiated next week but appointment panels, criteria and arrangements for the competition will only be approved at the March board. The board is the public authority which will initiate, manage and oversee the appointments processes."

Gerry Kelly said this was unfair on Ms Gillespie as she did not know about the change to job criteria when she decided to step down

He added that "it is my sincere hope that board members, regardless of whether they are political or independent members, will respect the governance of the board and will do nothing or say nothing that would undermine or jeopardise the impartiality and objectivity of the board in its significant responsibilities."

Mr Ford's plan to change the job criteria would have meant outgoing Deputy Chief Constable Gillespie was eligible to apply.

Gerry Kelly, the Sinn Fein justice spokesman and board member, said this was unfair on Ms Gillespie as she did not know about it when she decided to step down.

But Ms Gillespie said she already knew Mr Ford was considering changing the criteria.

In an email to PSNI staff and officers on Wednesday, she wrote: "I notified the Policing Board of my intention to retire before Christmas. This was a decision I made in quiet reflection over many months, considering a wide range of factors. In making this decision I was fully aware that a consultation process was already under way by the Justice Minister regarding the criteria for Chief Constable of PSNI."

Mr Ford was also criticised for taking a decision without consulting the justice committee.

But it emerged in a separate document that Mr Ford contacted the committee, but had "no response from any party to provide formal feedback either on the criteria or consultation process".

STORY SO FAR

Last month Judith Gillespie, the PSNI's Deputy Chief Constable, announced her intention to resign in March. This month Matt Baggott, the Chief Constable, announced he was also retiring this year.

Ms Gillespie was ineligible to succeed him because she had not served two years at Assistant Chief Constable level outside NI.

This week Justice Minister David Ford issued draft guidelines which would have eased the criteria by making such service desirable but not mandatory